The present invention relates to improvements in the second stage pressure regulators of a self-contained underwater breathing apparatus, popularly denoted by the acronym "scuba", and in particular to a device for manually adjusting, during a dive, the inhalation suction pressure required for opening the air inlet valve of the second stage regulator.
Compressed air, which is carried in cylinders by scuba divers, is expanded in two stages. First, the air is expanded through a pressure-reducing valve fixed to each of the cylinders. During this initial expansion, the pressure of the air is reduced from a high pressure, typically in excess of 2000 psi, to an intermediate pressure which is about 150 psi above ambient. Air at the intermediate pressure is then supplied through a flexible conduit or air supply hose to a second stage regulator where the air undergoes a further expansion.
In order to prevent the leakage of air during a dive, scuba divers use a breathing apparatus equipped with a demand-type, second stage regulator having an air inlet valve which remains closed, under the influence of spring biasing means, when the diver is not inhaling. In a typical second stage regulator, such as the one disclosed by Chambonnet, U.S. Pat. No. 4,798,202, a normally closed air inlet valve is mechanically levered to provide air flow when a diaphragm, which is exposed to ambient pressure, is pulled inwardly. This inward pull is provided by the combination of ambient pressure and suction created as a result of the diver's inhalation effort. The amount of suction necessary to open the valve varies inversely with the depth of a dive. At greater depths, increased water pressure causes the diaphragm to push more forcefully against the lever. Less suction is then required to open the valve.
Because of the variations in water pressure commonly experienced by scuba divers, the biasing means must be reset each time a diver plans to swim at a significantly different depth than on his last dive. Proper adjustment of the biasing means is thus critical. When a diver uses his breathing apparatus at a shallower depth than that for which it was adjusted, he must, in order to overcome the spring biasing means, inhale with considerably greater effort than is normally required. Conventional second stage regulators regulators are usually set to perform optimally at a depth of 90 feet. But with this setting, a diver finds that at shallow depths, he must supply 1 inch Hg or more vacuum cracking pressure, requiring very unnatural breathing, to open the air inlet valve. On the other hand, if a conventional second stage regulator were to be set for optimum performance near the surface, the air inlet valve would be free-flowing at 90 feet.
Most regulators, including Chambonnet's, must be disassembled before the biasing means can be reset. An exception is a regulator disclosed by Christianson in U.S. Pat. No. 4,862,884, having biasing means with both coarse and fine adjustment means, the latter being externally adjustable. Unfortunately, the range over which the biasing means in this prior art device can be finely tuned is quite limited. Moreover, Christianson's regulator must be disassembled in order to reset the coarse adjustment means. As a consequence, most divers must rely on qualified technicians at diving shops for assistance in resetting the biasing means.